How to prevent coarse grain ring defects in extruded aluminum profile products?

Coarse grain ring: Some aluminum alloy products, after quenching treatment and low-magnification inspection, show uneven grain size on the end face and particularly coarse grains around the periphery, forming a defect of a ring-like organization. The depth of the coarse grain ring increases closer to the tail end.

1. Causes of coarse grain ring in extruded aluminum profile products
   

(1) Inconsistent deformation during extrusion, metal is subjected to friction from the extrusion die wall, resulting in significant deformation and severe fragmentation of grains. During heat treatment heating, the surface layer grains grow significantly coarser;

(2) Too high quenching temperature or excessive holding time;

(3) Related to aluminum alloy composition and casting ingot structure.

2. Methods to eliminate coarse grain ring in extruded aluminum profile products
   

(1) Maintain a smooth inner wall of the extrusion die to form a complete aluminum sleeve, reducing friction during extrusion;

(2) Achieve as uniform deformation as possible (by controlling temperature, speed, etc.);

(3) Avoid excessively high quenching temperatures;

(4) Use a multi-hole mold for extrusion;

(5) Employ back extrusion and hydrostatic extrusion methods;

(6) Adjust the aluminum alloy composition to increase recrystallization inhibiting elements;

(7) Use higher temperatures for extrusion;

(8) Certain aluminum alloys undergo non-uniform treatment, resulting in a shallower coarse grain ring during extrusion.